The present invention relates to a highly transparent easily adhesive film and more specifically to a highly transparent easily adhesive film, which is a polypropylene film excellent in transparency and which is also excellent in the adhesion to a coated layer. The coated layer is excellent in the printability through the photogravure, relief printing, offset printing, flexography or the like, or capable of recording information through the ink jet recording technique.
A polypropylene film based on polypropylene, propylene copolymer or mixture thereof has widely been used as a film for packaging because of its excellent properties such as mechanical strength and transparency. On the other hand, it has been known that the polypropylene film has insufficient adhesion to a coated film applied onto the surface thereof. In this regard, the coated film is in general applied to the polypropylene film in order to impart various functions such as gas barrier properties, heat sealability and printability to the polypropylene film. This would be attributable to poor adhesive properties of the polypropylene film. There have been proposed a variety of means for eliminating this drawback, such as insertion of various anchor layers between the coated layer and the polypropylene film.
For instance, Japanese Examined Patent Publication No. Sho 45-32360 discloses a method, which makes use of a polyethyleneimine and a glycidyl type epoxy resin in such an anchor layer in order to improve the adhesive properties of a polypropylene film to a polyvinylidene chloride layer. The latter layer is applied to the polypropylene film for imparting gas barrier properties thereto. In addition, U.S. Pat. No. 3,023,126 discloses the use of an anchor layer comprising an isocyanate as a component thereof.
However, these methods have still been insufficient in the improvement of the adhesive properties of the polyolefin films and the use of only such an anchor layer has never permitted the printing operation with UV inks.
Accordingly, it is an object of the present invention to provide a highly transparent easily adhesive film, which can eliminate the foregoing drawbacks associated with the conventional techniques, more particularly, to provide the film which permits the production of a laminate film excellent in printability through, for instance, the photogravure, relief printing, offset printing and flexography, simply using an anchor layer. The film also has improved adhesion to a functional coated layer to be applied onto the anchor layer.
Another object of the present invention is to provide an adhesive sheet, which is an indicating label comprising a printable transparent film as a surface base material and which is used as a label for transparent containers. The adhesive sheet has an excellent ability of being printed through the conventional printing methods and is also excellent in adhesion to ink during the UV flexography, in transparency and is less susceptible to discoloration with light rays.
A still another object of the present invention is to provide a metal-deposited (for instance, aluminum-deposited) polyolefin film suitably used as, for instance, indicating labels.
According to a first aspect of the present invention, there is thus provided a laminate of films for printing, wherein an anchor layer containing an oxazoline group-modified resin is formed on the modified surface of a polyolefin film, at least one side of which is surface-modified.
According to a second aspect of the present invention, there is provided a laminate of films for printing, wherein at least one side of a longitudinally stretched polyolefin film is subjected to a corona discharge treatment, that an ethylene-acrylic acid type copolymer layer is formed on the corona discharge-treated surface, and that after the polyolefin film is stretched in the lateral direction, an anchor layer comprising a binder resin selected from the group consisting of acrylic resins, polyester resins and SBR resins and an oxazoline group-modified resin is applied onto the modified surface of the surface-modified polyolefin film, which has been subjected to the corona surface-treatment.
According to a third aspect of the present invention, there is further provided the foregoing laminate of films in which an adhesive layer is formed on the surface of the surface-modified polyolefin film opposite to the surface thereof to which the anchor layer is applied.
According to a fourth aspect of the present invention, there is provided the foregoing laminate of films in which an adhesive layer, for metal vapor-deposition, containing an anti-blocking agent is formed on the surface of the surface-modified polyolefin film opposite to the surface thereof to which the anchor layer is applied and a vapor-deposited metal layer is applied onto the adhesive layer.
According to a fifth aspect of the present invention, there is provided the foregoing laminate of films, in which the surface-modified polyolefin film is a surface-roughened polyolefin sheet and in which a vapor-deposited metal layer is present on the surface of the sheet opposite to that carrying the anchor layer.
According to a sixth aspect of the present invention, there is provided a method for preparing a laminate of films for printing. The method comprises the steps of subjecting, to a corona discharge treatment, at least one side of a longitudinally stretched polyolefin film; forming an ethylene-acrylic acid type copolymer layer on the corona discharge-treated surface of the polyolefin film; stretching the polyolefin film in the lateral direction; and then forming an anchor layer, which comprises a binder resin selected from the group consisting of acrylic resins, polyester resins and SBR resins and an oxazoline group-modified resin on the modified surface of the surface-modified polyolefin film, which has been subjected to the corona discharge treatment.
A biaxially oriented polyolefin film in which at least one side thereof is surface-modified is preferably used in the present invention.
This biaxially oriented polyolefin film in which at least one side thereof is surface-modified is prepared as follows: A polyolefin composition is melt-extruded according to the usual method and then the melt-extruded composition is first oriented in its longitudinal direction to give a uniaxially oriented film. Thereafter, the longitudinally oriented polyolefin film is further oriented in the lateral direction. The thickness of the film obtained after the lateral orientation is not restricted to any particular range, but it preferably ranges from 15 to 100 xcexcm. In general, the draw ratio: longitudinal/lateral orientation of the film preferably ranges from 2 to 10.
In the present invention, a layer is formed by applying ethylene-acrylic acid type copolymer paint onto at least one side of the film and then drying after the longitudinal orientation and before the lateral orientation to thus surface-modify the polyolefin film. In this respect, a film is in general longitudinally oriented while making use of the difference in the peripheral speed between rolls. For this reason, if the layer is applied before the longitudinal orientation of the film, the coated surface of the film comes in contact with the surface of these rolls during the longitudinal orientation. Accordingly, the film is not uniformly surface-modified and this in turn results in the reduction of adhesion to the anchor layer. On the other hand, the application of the layer after the lateral orientation of the film would leads to a decrease of the adhesion between the polyolefin composition and the ethylene-acrylic acid type copolymer.
In this respect, examples of methods for surface-modification are a corona discharge treatment and/or a flame treatment, with the corona discharge treatment being preferred. In addition, examples of the methods include surface-roughened methods (1) to (6) which will be described later.
As the polyolefin composition used in the present invention, there may be listed, for instance, polyethylene (irrespective of the density thereof), polypropylene and polybutene, with polypropylene being more preferred.
The term xe2x80x9cpolypropylenexe2x80x9d herein means not only homopolymer of propylene, but also copolymers of propylene with copolymerizable other monomers such as xcex1-olefins represented by ethylene, butene and 4-methylpentene, aromatic olefins represented by styrene, and dienes represented by butadiene; or any known blend of propylene homopolymers and/or copolymers and other polymers and/or copolymers inasmuch as the blend does not lose characteristic properties peculiar to the polypropylene film.
In this connection, the foregoing polyolefin composition may if necessary comprise other additives such as a lubricating agent, an antistatic agent, an antioxidant, a UV absorber and a pigment.
Examples of ethylene-acrylic acid type copolymers usable in the present invention are at least one member selected from the group consisting of ethylene-(meth)acrylic acid ester-(meth)acrylic acid copolymers and ethylene-(meth)acrylic acid ester-(meth)acrylic acid salt copolymers, ethylene-(meth)acrylic acid ester-maleic anhydride copolymers, and ethylene-glycidyl (meth)acrylic acid ester copolymers.
The ethylene-acrylic acid type copolymer is preferably a random copolymer and 30 to 90% by weight of the components thereof is preferably occupied by ethylene moiety. In addition, the (meth)acrylic acid salt is not limited to any specific one in so far as they are metal salts and may be, for instance, sodium, potassium, calcium, lithium, magnesium and barium salts.
The ethylene-acrylic acid type copolymer is preferably converted into an aqueous paint by any known compulsory emulsification method. The ethylene-acrylic acid type copolymer paint may comprise a pigment for preventing any occurrence of blocking. The method for applying the ethylene-acrylic acid type copolymer paint is not restricted to any particular one and the paint may thus be applied according to any known method. Examples of such application methods are a Meyer bar coating method, a gravure coating method, a micro-gravure coating method, a die coating method, a blade coating method, a micro-rod coating method, an air knife coating method, a curtain coating method, a slide coating method and a roll coating method, but the coating method is not restricted to these specific ones.
The coated amount of the ethylene-acrylic acid type copolymer as determined after the lateral orientation preferably ranges from 0.01 to 1 g/m2 in the present invention.
Regarding the pigment included in the polyolefin film, at least one side of which is surface-modified, used in the present invention, it is preferred that the amount of the pigment be not more than 2000 ppm (0.2% by weight) for the polyolefin composition. On the other hand, the amount of the pigment preferably ranges from 0.1 to 10% by weight for the ethylene-acrylic acid type copolymer, which constitutes the modifying layer. More preferably, it is not more than 300 ppm for the polyolefin composition and 0.5 to 5% by weight for the modifying layer or the ethylene-acrylic acid type copolymer.
The pigment used in the present invention is not restricted to any particular one and may be any known inorganic pigments and organic pigments. Examples of inorganic pigments include kaolin, silica, calcium carbonate, aluminum hydroxide, talc, zeolite, mica powder and titanium oxide. On the other hand, examples of organic pigments are acrylic, styrenic, polyolefinic pigments and copolymers thereof. The organic pigments may be crosslinked ones for imparting solvent-insolubility to the pigments.
In the present invention, an anchor layer is formed on the polyolefin film, at least one side of which is surface-modified. The anchor layer may be formed on one or both sides thereof.
The principal component of the anchor layer used in the present invention is an oxazoline group-modified resin which may be optionally used with a binder resin. The anchor layer preferably comprises an oxazoline group-modified resin and a binder resin, more preferably consists of them.
The oxazoline group-modified resin is preferably present in the anchor layer in an amount ranging from 2 to 50% by weight and more preferably 5 to 20% by weight.
The term xe2x80x9coxazoline group-modified resinxe2x80x9d herein means any resin in which oxazoline groups are present. Examples thereof include acrylic resins, polyester resins, SBR resins, and polyolefin resins to which oxazoline groups are graft-bonded.
The binder resin as a component of the anchor layer may be at least one member selected from the group consisting of, for instance, acrylic resins, polyester resins and SBR resins.
In the present invention, the coated amount of the anchor layer preferably ranges from 0.05 g/m2 to 1 g/m2. The coated amount thereof more preferably ranges from 0.1 g/m2 to 0.5 g/m2.
The anchor layer may comprise a pigment for inhibiting the occurrence of any blocking. The amount of the pigment to be incorporated into the anchor layer is preferably not more than 5% by weight.
In the present invention, a functionality-imparting layer may be formed on the anchor layer of the highly transparent and easily adherent film prepared according to the foregoing procedures, depending on various purposes.
The functionality-imparting layer is not restricted to specific ones inasmuch as they can impart desired functions to the transparent adhesive film and they may be either transparent or opaque. For instance, a layer capable of forming characters, images or the like on the film may be applied onto the anchor layer by applying, through printing, a layer with an ink such as a UV ink, a gravure printing ink and a thermal transfer ink.
Moreover, a heat-sensitive recording medium can be produced by applying, onto the highly transparent and easily adherent film, a recording layer such as a layer having a heat-sensitive recording ability or a heat-sensitive recording layer, which comprises, for instance, a leuco dye, a developer and/or a sensitizer. Such a heat-sensitive layer may be applied onto the film according to any known method and it is a matter of course to apply an under coat layer and/or an overcoat layer onto the heat-sensitive recording layer. Examples of such functionality-imparting layers further include those possessing abilities of ink-jet recording, melt thermal transfer recording, thermal sublimation transfer recording, electrostatic recording, pressure-sensitive recording, PPC recording and magnetic recording, as well as printing ink-receiving layers.
In the present invention, the film may be subjected to a corona discharge treatment and/or a flame treatment even in any step (after longitudinal orientation, after lateral orientation, before and after application of an anchor layer, before and after application of a functionality-imparting layer and/or before and after printing).
In the present invention, the resulting highly transparent and easily adherent film may be subjected to an overlaminating treatment according to any known method. Alternatively, the resulting film may be subjected to any fabricating treatment such as a treatment in which the film is used as surface paper and it is laminated with an adhesive layer and/or a release sheet to thus give an adhesive sheet. In the present invention, however, any fabricating treatment usable herein is not restricted to specific ones.
In case the foregoing film laminate (an adhesive sheet) wherein an adhesive layer is formed on the side of the surface-modified polyolefin film opposite to the side onto which an anchor layer is applied, according to the present invention, a release sheet is preferably applied onto the adhesive layer. In addition, if the resulting adhesive sheet is used as an indicating label, the thickness of the polyolefin film desirably ranges from about 20 to 200 xcexcm and preferably about 20 to 100 xcexcm.
An adhesive used in the present invention as a constituent is not restricted to any specific one and may be, for instance, a rubber type, acrylic, vinyl ether type, urethane type or silicone type one, which may be in the form of a solution, an emulsion or a hot melt. In particular, acrylic adhesives comprising, as principal components, acrylic premonomers, acrylic monomers or the like are preferably used in the present invention, from the viewpoint of their transparency and weatherability.
Such an acrylic adhesive is not restricted to any particular one and examples thereof are acryl group-containing vinyl monomers, epoxy group-containing vinyl monomers, alkoxy group-containing vinyl monomers, ethylene oxide group-containing vinyl monomers, amino group-containing vinyl monomers, amido group-containing vinyl monomers, halogen atom-containing vinyl monomers, phosphate residue-containing vinyl monomers, sulfonate residue-containing vinyl monomers, silane group-containing vinyl monomers, phenyl group-containing vinyl monomers, benzyl group-containing vinyl monomers, tetrahydrofurfuryl group-containing vinyl monomers and other copolymerizable monomers. The foregoing acrylic resins are polymerized by any method such as the bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization in which a water-insoluble of hardly water-soluble monomer is dispersed in water together with an emulsifying agent, followed by polymerization thereof in the presence of a water-soluble initiator. Among the acrylic resins prepared by these methods, preferred be adhesives prepared by the emulsion polymerization. This is because the emulsion polymerization permits the achievement of a high cohesive force without using any crosslinking agent and the polymerization method permits the saving of energy and is not harmful to the environment.
A variety of additives may if necessary be incorporated into these acrylic adhesives for the improvement of the adhesive properties thereof. Examples of such additives are adhesiveness-imparting agents, for instance, naturally occurring resins such as rosin, modified rosin, rosin and modified rosin derivatives, polyterpene resins, modified terpene, aliphatic hydrocarbon resins, cyclopentadiene resins, aromatic petroleum resins, phenol resins, alkyl-phenol-acetylene resins, cumarone-indene resins and vinyl toluene-xcex1-methylstyrene copolymers; age-resistors; stabilizers; softening agents such as oils; and fillers. These additives may be used alone or in any combination of at least two of them. Moreover, it is also possible to add, to the adhesive layer, an organic UV absorber such as a benzophenone type or benzotriazole type one in order to improve the weatherability thereof.
The adhesive layer can be formed by applying the foregoing adhesive to a release sheet, drying the coated adhesive if necessary to form an adhesive layer and then combining the adhesive layer with a surface base material. Thus, an adhesive sheet according to the present invention can be prepared. This adhesive layer may be applied using a device such as a reverse roll coater, a knife coater, a bar coater, a slot die coater, an air knife coater, a reverse gravure coater and a variogravure coater. The coated amount of the adhesive weighed after drying is preferably adjusted to the range of from 5 to 50 g/m2 and more preferably 10 to 30 g/m2. This is because if the coated amount of the adhesive is less than 5 g/m2, the adhesive force of the adhesive to the adherend becomes insufficient. On the other hand, if it exceeds 50 g/m2, the coated adhesive may squeeze out and the resulting product may have insufficient printability.
The release sheet applied for covering the adhesive layer is not restricted to any particular one. Examples thereof conveniently used herein are a dense substratum such as glassine paper, clay-coated paper, paper obtained by laminating kraft paper or wood free paper with a film such as a polyethylene film, paper obtained by coating wood free paper with, for instance, polyvinyl alcohol or an acrylic acid ester copolymer resin, those obtained by applying, for instance, a fluoroplastic or a silicone resin onto a plastic film such as polyethylene terephthalate or polypropylene in an amount, weighed after drying, of 0.05 to 3 g/m2 and then subjecting the resin to thermosetting, electron radiation curing or the like to form a release layer.
The release layer may conveniently be applied using a coating device such as a bar coater, an air knife coater, a direct gravure coater, an offset gravure coater, or a multi-stage roll coater. In this respect, a release sheet comprising a plastic film rather than a paper-type release sheet is preferably used in case where high transparency is required, from the viewpoint of the transparency and surface smoothness. Moreover, a release sheet comprising a plastic film is preferred as compared with the paper-type one since the former is not susceptible to temperature and humidity and hardly causes curling as compared with the latter.
The adhesive sheet thus prepared after removing the release sheet of a plastic film or the structure comprising the surface base material and the adhesive layer preferably has a haze value of not more than 5.0%.
According to the present invention, there is also provided a film laminate which comprises a surface-modified polyolefin film carrying an anchor layer on one side thereof, an adhesive layer for vapor depositing a metal applied onto the side of the polyolefin film opposite to the anchor layer-carrying side and a vapor-deposited metal layer containing a blocking-inhibitory agent on the adhesive layer. In this regard, the laminate preferably has an adhesive layer such as that discussed above on the vapor-deposited metal layer.
As such an adhesive layer (an adhesive layer for a vapor-deposited metal layer) for improving the adhesion of the film to the vapor-deposited metal layer, it is sufficient to use a layer obtained by applying a resin (compound), which permits the improvement of the adhesion of the vapor-deposited metal layer. More specifically, preferably used herein are an acrylic polyol and a vinyl chloride-vinyl acetate copolymer; an ethyleneimine polymer and polyethyleneimine-containing methacrylic acid ester compound; and nitrocellulose and acrylic polyol resin. Such an adhesive layer may preferably be used herein because of its excellent adhesion and water resistance. In this regard, auxiliary agents such as a curing agent and a UV absorber may be added to the adhesive layer for vapor deposition. In particular, it is preferred to promote crosslinking through the addition of an isocyanate compound to acrylic polyol and vinyl chloride-vinyl acetate copolymer, since the adherence of the resulting adhesive layer is further improved.
In the present invention, when winding up the film on which the foregoing adhesive layer for vapor-deposition (the film is once wound up prior to the vapor-deposition), a blocking-inhibitory agent is in advance incorporated into the adhesive layer for vapor-deposition in order to prevent the occurrence of any blocking due to the contact between the easily printable layer and the adhesive layer for vapor-deposition.
The blocking-inhibitory agent is not restricted to any particular one inasmuch as it can prevent the occurrence of any blocking. However, preferably used herein are organic pigments and inorganic pigments since the addition thereof in only a small amount can inhibit any blocking. The organic and inorganic pigments usable in the present invention are not restricted to particular ones insofar as they never impair the transparency of the resulting film. However, particularly preferred are organic pigments having approximately true spherical shapes (extending from true spherical shapes to spherical shapes close to the true spherical shapes). Particularly preferred examples of such organic pigments include acrylic resins, polystyrene resins, and styrene-acrylic copolymer resins. Among these, polymethacrylate crosslinked products (acrylic resins) are particularly preferred because of their excellent transparency. The relative amount of the pigment (organic pigment) to be incorporated into the adhesive layer for vapor-deposition preferably ranges from 0.1 to 1.0 part by weight and particularly preferably 0.2 to 0.5 part by weight based on 100 parts by weight of the solid contents of the adhesive layer. In addition, the particle size of the organic pigment is not limited to any specific range, but it preferably ranges from 1.0 to 10 xcexcm.
The adhesive layer for metal vapor-deposition may be formed by diluting the foregoing components with a solvent such as toluene, ethyl acetate, IPA or MEK to a desired extent and then applying the resulting dispersion onto the film by any known coating method. Examples of such known coating method include a metering bar coating, gravure roll coating, air knife coating, spray coating or reverse roll coating method.
The thickness of the adhesive layer for metal vapor-deposition is not restricted to any particular range inasmuch as it can ensure satisfactory adhesion of the layer to the metal vapor-deposited layer. However, if the thickness is too high, the production cost increases and the resulting product would be liable to cause blocking. Therefore, the adhesive layer is desirably formed in a thickness of not more than about 3.0 xcexcm and preferably not more than about 1.5 xcexcm. In this connection, it is also possible to simultaneously form the easily printable layer and the adhesive layer for metal vapor-deposition by applying ingredients for these layers at the same time.
Alternatively, such an adhesive layer for vapor-deposition may likewise be prepared by coating a resin for improving adhesiveness on the easily adherent film after longitudinal orientation of the film and then subjecting the film to lateral orientation. Such a method is quite preferred since it permits the formation of an adhesive layer having high transparency. More specifically, a polyolefin composition is melt-extruded according to the usual method and then the extruded polyolefin composition is first longitudinally stretched to give a film uniaxially oriented in the longitudinal direction. At this stage, either or both sides of the resulting longitudinally uniaxially oriented film may be subjected to a corona discharge treatment and/or a flame treatment for the improvement of the wet tension of the face(s). Thereafter, a blocking-inhibitory agent-containing adhesive layer for vapor-deposition is applied onto the face. The coated layer is sufficiently dried prior to the lateral orientation. In this respect, the resin coated layer on the film obtained after the lateral orientation may further be subjected to a corona discharge treatment. The resin to be applied is preferably an ethylene-acrylic acid type copolymer and the latter is used in the form of an aqueous dispersion or solution.
In addition, a coating liquid can be applied onto the both sides of the film after the longitudinal orientation, followed by drying and lateral orientation. Thus, the resin films formed on the both sides of the film can serve as an anchor layer for easy printing on the one side and an adhesive layer for vapor-deposition on the other side.
The haze value of the film prior to the vapor-deposition of a metal is preferably not more than 5% and more preferably not more than 3%.
In this connection, it is also possible to impart a color tone, which cannot be achieved by simple vapor-deposition of a metal by incorporating a coloring agent (such as a dye) into at least one layer selected from the film base material, the adhesive layer for vapor-deposition and the easily printable layer.
As methods for depositing a metal on the adhesive layer for vapor-deposition in vacuo, the vacuum deposition technique usually employed can be used without any modification. Examples of metals usable in the present invention are aluminum, gold, silver, copper, chromium, tin, indium, antimony, and nickel, with aluminum being most generally used. For instance, it is sufficient to vapor-deposit, with heating, a metal onto one side of a base film material in a container which is evacuated to a high vacuum. The depositing method may be a small-sized batchwise method and a continuous method in which a metal is vapor-deposited on a film wound into a roll-like shape. The thickness of the aluminum thus deposited in general ranges from 20 A to 1000 A and preferably not more than 500 A.
In the present invention, an adhesive layer and a release sheet can be laminated with the vapor-deposited film on the side on which the metal has been vapor-deposited. Alternatively, it is also possible to first form a resin layer for protecting the vapor-deposited layer on the surface thereof and to then laminate the resin layer with an adhesive layer.
The present invention also provides the foregoing film laminate in which the surface-modified polyolefin film is a surface-roughened polyolefin sheet and a metal vapor-deposited layer is formed on the side of the sheet opposite to the anchor layer-carrying side of the sheet. In this case, the foregoing adhesive layer is preferably applied onto the metal vapor-deposited layer.
A polyolefin film such as a polypropylene film can in general be surface-roughened by, for instance, the following methods: (1) A method comprises for embossing a film, (2) A method comprises the step of spraying fine particles such as sand particles to the surface of a film to thus form small defects on the film surface (sand-matting method), and (3) A method comprises the step of forming unevenness on the film surface through coating.
Examples of other surface-roughening treatments of the polyolefin film include the following methods: (4) A method comprises the steps of laminating a polypropylene resin film with a resin composition containing an ethylene-propylene block copolymer and then orienting the resulting laminate, (5) A method comprises the steps of laminating a polypropylene film with a resin composition blended with a polyethylene and then orienting the resulting laminate, and (6) A method comprises the steps of preparing a sheet by extruding a mixture of polypropylenes different in crystallizability and then stretching the resulting sheet.
In the present invention, a method in which a resin is laminated with a polyolefin film and then oriented, like the latter method (such as the foregoing method (4), (5) or (6)) are particularly preferred. This is because, the film can be surface-roughened during production of the film and therefore, the method does not require the use of other steps such as embossing and sand matting. Moreover, the method also permits the formation of a roughened surface having excellent matting properties. The method (5) is particularly preferred among others. This is because the incorporation of polyethylene would greatly enhance the adhesion of the metal vapor-deposited layer to the polyolefin film. In addition, if the both sides of the polyolefin film are surface-roughened, the resulting product has further improved matting properties as compared with the product, only one side of which is surface-roughened.
An adhesive layer for vapor-deposition may be formed to improve the adhesion between the film and the metal vapor-deposited layer (for instance, deposited aluminum layer). Preferably used herein as such an adhesive layer for vapor-deposition are those described above. The adhesive layer may be applied to a roughened surface or a smooth surface. In this connection, the smooth surface is insufficient in particular in the adhesion to the metal vapor-deposited layer and thus an adhesive layer is preferably used. The adhesive layer may be one obtained by coating a resin (compound), which allows the improvement of the adhesion the film to the vapor-deposited metal layer. The thickness of the adhesive layer thus applied should preferably be not more than 1.5 xcexcm. This is because if the application of such a resin in an excess amount may result in an increase of the production cost and the occurrence of blocking phenomenon. Alternatively, when an adhesive layer is applied onto a roughened surface, the thickness of the adhesive layer is preferably not more than 1.5 xcexcm.
The present invention will hereunder be described in more detail with reference to the following working Examples, but the present invention is not restricted to these specific Examples at all. In each Example given below, xe2x80x9c%xe2x80x9d means xe2x80x9c% by weightxe2x80x9d.